U.S. patent application number 16/048567 was filed with the patent office on 2019-03-28 for image forming apparatus.
This patent application is currently assigned to Ricoh Company, Ltd.. The applicant listed for this patent is Koichi Murota, Susumu Narita, Hiroaki Nishina, TAKUMA NISHIO, Yoshinobu Sakaue, Ryo Sato, Masashi Suzuki. Invention is credited to Koichi Murota, Susumu Narita, Hiroaki Nishina, TAKUMA NISHIO, Yoshinobu Sakaue, Ryo Sato, Masashi Suzuki.
Application Number | 20190094776 16/048567 |
Document ID | / |
Family ID | 65807464 |
Filed Date | 2019-03-28 |
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United States Patent
Application |
20190094776 |
Kind Code |
A1 |
NISHIO; TAKUMA ; et
al. |
March 28, 2019 |
IMAGE FORMING APPARATUS
Abstract
An image forming apparatus includes an image reading device; an
image forming device including a photoconductor, a charger, an
exposure device including a light-emitting element, a memory to
store a first correction value for correction a light emission
amount of the light-emitting element, and a driver to drive the
light-emitting element, a developing device, a transfer device, and
a fixing device. The image forming apparatus further includes a
processor to calculate a second correction value for correcting the
light emission amount, based on density data of image data of a
predetermined pattern on a recording medium; calculate a third
correction value for correcting the light emission amount, based on
the first correction value and the second correction value; and
determine, before calculating the third correction value, whether
placement of the recording medium on the reading table is correct
based on the density data.
Inventors: |
NISHIO; TAKUMA; (Kanagawa,
JP) ; Sakaue; Yoshinobu; (Kanagawa, JP) ;
Narita; Susumu; (Tokyo, JP) ; Sato; Ryo;
(Tokyo, JP) ; Murota; Koichi; (Tokyo, JP) ;
Suzuki; Masashi; (Saitama, JP) ; Nishina;
Hiroaki; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NISHIO; TAKUMA
Sakaue; Yoshinobu
Narita; Susumu
Sato; Ryo
Murota; Koichi
Suzuki; Masashi
Nishina; Hiroaki |
Kanagawa
Kanagawa
Tokyo
Tokyo
Tokyo
Saitama
Tokyo |
|
JP
JP
JP
JP
JP
JP
JP |
|
|
Assignee: |
Ricoh Company, Ltd.
Tokyo
JP
|
Family ID: |
65807464 |
Appl. No.: |
16/048567 |
Filed: |
July 30, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03G 15/228 20130101;
H04N 1/6041 20130101; H04N 1/605 20130101; H04N 1/00779 20130101;
H04N 1/0473 20130101; H04N 1/506 20130101; H04N 1/00702 20130101;
H04N 1/053 20130101; H04N 1/00771 20130101; G03G 15/04054 20130101;
H04N 1/6033 20130101; H04N 1/48 20130101; H04N 1/00763
20130101 |
International
Class: |
G03G 15/22 20060101
G03G015/22; H04N 1/00 20060101 H04N001/00; H04N 1/053 20060101
H04N001/053; H04N 1/047 20060101 H04N001/047; G03G 15/04 20060101
G03G015/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 25, 2017 |
JP |
2017-184079 |
Claims
1. An image forming apparatus comprising: an image reading device
including a reading table, the image reading device to generate
image data from reading of a pattern on a recording medium placed
on the reading table; an image forming device including: a
photoconductor; a charger to charge a surface of the
photoconductor; an exposure device to expose the charged surface of
the photoconductor to form an electrostatic latent image on the
photoconductor, the exposure device including: a light-emitting
element; a memory to store a first correction value for correcting
a light emission amount of the light-emitting element; and a driver
to drive the light-emitting element; and a developing device to
supply toner to the electrostatic latent image to form a toner
image; a transfer device to transfer the toner image onto a
recording medium; and a fixing device to fix the toner image on the
recording medium; and a processor configured to: cause the image
forming device to form a predetermined pattern on the recording
medium and cause the image reading device to generate the image
data of the predetermined pattern; calculate a second correction
value for correcting the light emission amount, based on density
data acquired from the image data of the predetermined pattern;
calculate a third correction value based on the first correction
value and the second correction value, the third correction value
for correcting the light emission amount; and determine, before
calculating the third correction value, whether placement of the
recording medium on the reading table is correct based on the
density data.
2. The image forming apparatus according to claim 1, wherein the
processor is configured not to calculate the third correction value
in response to a determination result that the placement of the
recording medium is not correct.
3. The image forming apparatus according to claim 1, further
comprising a display, wherein the processor is configured to
indicate an error on the display in response to a determination
result that the placement of the recording medium is not
correct.
4. The image forming apparatus according to claim 1, wherein the
predetermined pattern includes a continuous region that extends
continuously in a main scanning direction at a time of formation of
the predetermined pattern.
5. The image forming apparatus according to claim 4, wherein the
processor is configured to change a length of the continuous region
in the main scanning direction corresponding to a size of the
recording medium on which the predetermined pattern is to be
formed.
6. The image forming apparatus according to claim 1, wherein the
processor is configured to cause the image forming device to form
the predetermined pattern at a position shifted from a center in a
sub-scanning direction at a time of formation of the predetermined
pattern.
7. The image forming apparatus according to claim 1, wherein the
processor is configured to set a position of the predetermined
pattern avoiding a shock jitter area in formation of the
predetermined pattern.
8. The image forming apparatus according to claim 1, wherein the
processor is configured to: set, on the reading table, a pattern
presence determination area in which the predetermined pattern is
present on the recording medium being placed at a correct position
on the reading table; determine whether the density data
corresponding to the pattern presence determination area is smaller
than a threshold; and determine that the placement of the recording
medium is not correct in response to a determination result that
the density data is smaller than the threshold.
9. The image forming apparatus according to claim 1, wherein the
processor is configured to: set, on the reading table, a pattern
absence determination area in which the predetermined pattern is
not present on the recording medium being placed at a correct
position on the reading table; determine whether the density data
corresponding to the pattern absence determination area is greater
than a threshold; and determine that the placement of the recording
medium is not correct in response to a determination result that
the density data is greater than the threshold.
10. The image forming apparatus according to claim 1, wherein the
predetermined pattern is smaller than the recording medium in a
main scanning direction and a boundary of the predetermined pattern
in the main scanning direction at a time of formation of the
predetermined pattern is present on the recording medium, wherein
the processor is configured to: set, on the reading table, a first
boundary area and a second boundary area to overlap the boundary of
the predetermined pattern on the recording medium being placed at a
correct position on the reading table, the second boundary area
different from the first boundary area in position in the main
scanning direction and similar to the first boundary area in
position in a sub-sub-scanning direction; acquire first boundary
density data including density data of a plurality of pixels of the
first boundary area; acquire second boundary density data including
density data of a plurality of pixels of the second boundary area;
calculate a density change position representing a pixel at which a
density value changes in each of the first boundary density data
and the second boundary density data; compare the density change
position in the first boundary density data and the density change
position in the second boundary density data; and determine that
the placement of the recording medium is not correct in response to
a comparison result indicating that a difference between the
density change position in the first boundary density data and the
density change position in the second boundary density data exceeds
a predetermined range.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is based on and claims priority
pursuant to 35 U.S.C. .sctn. 119(a) to Japanese Patent Application
No. 2017-184079, filed on Sep. 25, 2017, in the Japan Patent
Office, the entire disclosure of which is hereby incorporated by
reference herein.
BACKGROUND
Technical Field
[0002] The present disclosure relates to an image forming
apparatus.
Description of the Related Art
[0003] In a light emitting diode (LED) head, variations in shape
and characteristics of LED elements, minute misalignment in LED
chips, or periodic or aperiodic fluctuations in optical
characteristics of a lens array cause density unevenness. Such
density unevenness occurs as vertical streaks or bands extending
perpendicular to the arrangement direction of the LED elements,
degrading image quality.
[0004] To correct such vertical streaks and vertical bands
resulting from the LED head, the following approach is known. A
predetermined pattern for density detection is formed with an image
forming apparatus for testing an LED head, and the pattern is read
with a scanner. Based on the image density of the pattern,
correction values for reducing vertical stripes and vertical bands
are calculated and recorded in a memory of the LED head to be used
in printing.
SUMMARY
[0005] According to an embodiment of this disclosure, an image
forming apparatus includes an image reading device including a
reading table. The image reading device generates image data from
reading of a pattern on a recording medium placed on the reading
table. The image forming apparatus further includes an image
forming device including a photoconductor, a charger to charge a
surface of the photoconductor, an exposure device to expose the
charged surface of the photoconductor to form an electrostatic
latent image on the photoconductor, a developing device to supply
toner to the electrostatic latent image to form a toner image, a
transfer device to transfer the toner image onto a recording
medium, and a fixing device to fix the toner images on the
recording medium. The exposure device includes a light-emitting
element, a memory to store a first correction value for correcting
a light emission amount of the light-emitting element, and a driver
to drive the light-emitting element. The image forming apparatus
further includes a processor configured to cause the image forming
device to form a predetermined pattern on the recording medium and
cause the image reading device to generate the image data of the
predetermined pattern; calculate a second correction value for
correcting the light emission amount, based on density data
acquired from the image data of the predetermined pattern;
calculate a third correction value for correcting the light
emission amount, based on the first correction value and the second
correction value; and determine, before calculating the third
correction value, whether placement of the recording medium on the
reading table is correct based on the density data.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] A more complete appreciation of the disclosure and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0007] FIG. 1 is a schematic cross-sectional view of an image
forming apparatus according to an embodiment;
[0008] FIG. 2 is a schematic diagram illustrating an example
structure of an image forming unit 50 and periphery in the image
forming apparatus illustrated in FIG. 1;
[0009] FIG. 3 is a schematic diagram illustrating an example of a
detailed configuration of an exposure device according to an
embodiment;
[0010] FIG. 4 is a schematic view of another example structure of
the image forming unit and the periphery thereof;
[0011] FIG. 5 is a schematic diagram illustrating another example
of the detailed configuration of the exposure device;
[0012] FIG. 6 is a schematic block diagram illustrating a hardware
configuration of the image forming apparatus illustrated in FIG.
1;
[0013] FIG. 7 is a functional block diagram of the image forming
apparatus illustrated in FIG. 1;
[0014] FIG. 8 is a flowchart illustrating a processing flow to
print a density acquisition pattern, according to an
embodiment;
[0015] FIG. 9 is a flowchart illustrating a flow of operation to
acquire density data from the density acquisition pattern,
according to an embodiment;
[0016] FIG. 10 is a flowchart illustrating an operation flow of
image formation based on the density correction according to an
embodiment;
[0017] FIGS. 11A and 11B are graphs illustrating image density
distributions in a main scanning direction of an output result
based on a first correction value of the density acquisition
pattern and an output result based on a third correction value
according to an embodiment;
[0018] FIG. 12 is a schematic view of a recording medium on which a
density acquisition pattern according to an embodiment is
printed;
[0019] FIG. 13 is a flowchart illustrating a flow of operation to
determine abnormality in reading according to an embodiment;
[0020] FIG. 14 illustrates an example of a density acquisition
pattern formation area and abnormality determination areas
(placement error) according to an embodiment;
[0021] FIG. 15 is a flowchart illustrating an example of detection
of incorrect sheet placement according to an embodiment;
[0022] FIG. 16 illustrates another example of the density
acquisition pattern formation area and the abnormality
determination area;
[0023] FIG. 17 is an enlarged view of third and fourth abnormality
determination areas according to an embodiment;
[0024] FIG. 18 is a flowchart illustrating another example of
detection of incorrect sheet placement according to an
embodiment;
[0025] FIGS. 19A and 19B illustrate first explanatory examples of
placement of the recording medium and determination results of the
placement;
[0026] FIGS. 20A and 20B illustrate second explanatory examples of
placement of the recording medium and determination results of the
placement;
[0027] FIGS. 21A and 21B illustrate third explanatory examples of
placement of the recording medium and determination results of the
placement; and
[0028] FIGS. 22A and 22B illustrate example density acquisition
patterns considering shock jitter.
[0029] The accompanying drawings are intended to depict embodiments
of the present invention and should not be interpreted to limit the
scope thereof. The accompanying drawings are not to be considered
as drawn to scale unless explicitly noted.
DETAILED DESCRIPTION
[0030] In describing embodiments illustrated in the drawings,
specific terminology is employed for the sake of clarity. However,
the disclosure of this patent specification is not intended to be
limited to the specific terminology so selected, and it is to be
understood that each specific element includes all technical
equivalents that operate in a similar manner and achieve a similar
result.
[0031] Referring now to the drawings, wherein like reference
numerals designate identical or corresponding parts throughout the
several views thereof, and particularly to FIG. 1, an image forming
apparatus according to an embodiment of this disclosure is
described. As used herein, the singular forms "a", "an", and "the"
are intended to include the plural forms as well, unless the
context clearly indicates otherwise.
[0032] The suffixes Y, M, C, and K attached to each reference
numeral indicate only that components indicated thereby are used
for forming yellow, magenta, cyan, and black images, respectively,
and hereinafter may be omitted when color discrimination is not
necessary.
[0033] FIG. 1 is a schematic side view of an image forming
apparatus 1 incorporating a scanner 100. The image forming
apparatus 1 is a multifunction peripheral (MFP) having a plurality
of functions such as a copy function, a facsimile (FAX) function, a
print function, a scanner function, storing of an input image (an
image of a document scanned or an image input by the print function
or the facsimile function), and distribution of the input image.
The image forming apparatus 1 includes the scanner 100 as an image
reading device, an image forming device 200, and a sheet feeder
300.
[0034] The scanner 100 includes an exposure glass 11 as a reading
table and a reading unit 12. The reading unit 12 includes a light
source 12-1, a mirror 12-2, and a sensor 12-3. Light from the light
source 12-1 is directed onto a recording medium such as a paper
sheet placed on the exposure glass 11. The light reflected on the
recording medium is further reflected by the mirror 12-2 toward the
sensor 12-3. Based on the light received, the sensor 12-3 generates
image data. The scanner 100 can further include an automatic
document feeder (ADF) 13. The ADF 13 automatically conveys the
recording medium onto the exposure glass 11 with a sheet feeding
roller.
[0035] The image forming device 200 includes an exposure device 14
and image forming units 50Y, 50M, 50C, and 50K (hereinafter simply
"image forming unit 50" when color discrimination is not
necessary). The image forming units 50 include photoconductor drums
15Y, 15M, 15C, and 15K (hereinafter simply "photoconductor drum 15"
when color discrimination is not necessary).
[0036] The exposure device 14 exposes the photoconductor drum 15 to
form a latent image, based on image data read from the document by
the scanner 100 and a print instruction received from an external
device. As will be described later, the image forming units 50
supplies different color toners, respectively, to the
photoconductor drums 15 to develop the latent images into toner
images. The toner images are then transferred from the
photoconductor drums 15 via a transfer belt 17 onto the recording
medium fed by the sheet feeder 300, after which a fixing device 18
fuses and fixes the superimposed toner images on the recording
medium.
[0037] The sheet feeder 300 includes sheet feeding trays 19 and 20
to accommodate different size recording media and a feeder 21 to
feed the recording medium from the sheet feeding tray 19 or 20 to
an image formation position in the image forming device 200. The
feeder 21 includes various types of rollers.
[0038] FIG. 2 is a schematic diagram illustrating an example
structure of the image forming unit 50 and periphery thereof. FIG.
2 is a cross-sectional view of the periphery of the image forming
unit 50 viewed from a side. Operations common to the image forming
units 50 will be described using the image forming unit 50Y as a
representative.
[0039] The image forming unit 50Y includes the photoconductor drum
15Y as an image bearer. Further, a charging device 51Y (a charger),
a developing device 52Y, a transfer device 53Y, a cleaning device
54Y, and a discharge device 55Y are disposed around the
photoconductor drum 15Y. Between the charging device 51Y and the
developing device 52Y in the direction of rotation of the
photoconductor drum 15Y, a light-emitting diode (LED) array head
61Y of the exposure device 14 is disposed. The LED array head 61Y
is a light source. The LED array head 61Y is configured to expose
the photoconductor drum 15Y. The LED array head 61Y can be
incorporated in the image forming unit 50Y.
[0040] To form images, the charging device 51Y uniformly charges
the surface of the photoconductor drum 15Y in the dark, after which
the LED array head 61Y exposes the surface of the photoconductor
drum 15 with light corresponding to a yellow image, thus forming an
electrostatic latent image thereon. The developing device 51Y
develops (visualizes) the electrostatic latent image with yellow
toner. As a result, a yellow toner image is formed on the
photoconductor drum 15Y. The yellow toner image is then transferred
from the photoconductor drum 15Y onto the transfer belt 17, which
is looped around rollers 22, 23 and 24 and rotates clockwise in the
drawing.
[0041] Similar to the image forming unit 50Y, in the image forming
units 50M, 50C, and 50K, the toner images are sequentially
transferred from the respective photoconductor drums 15M, 15C, and
15K onto the transfer belt 17. Thus, four color images are
superimposed on the transfer belt into a multi-color image. Then, a
secondary transfer unit 26 (see FIG. 2) transfers the image from
the transfer belt 17 onto the recording medium, which is conveyed
to the secondary transfer unit 26 as indicated by arrow YP
illustrated in FIG. 2. Then, the four-color superimposed image is
formed on the recording medium. Then, in the fixing device 18, the
image is fixed on the recording medium with heat and pressure. The
recording medium on which the image has been fixed is discharged
outside the image forming apparatus 1. After the transferring, a
cleaning device 25 removes residual toner remaining untransferred
on the transfer belt 17.
[0042] FIG. 3 is a perspective view of the LED array head 61 and
the periphery thereof. The LED array head 61 is a unit including an
LED array 62 and a lens array 61 The LED array 62 includes a
substrate and a plurality of LED array elements mounted on the
substrate and lined in a main scanning direction (indicated by
arrow AR1 in FIG. 3) which is perpendicular to a sub-scanning
direction identical to a direction in which the recording medium is
conveyed (indicated by hollow arrow in FIG. 3). The main scanning
direction is perpendicular to the direction of rotation of the
photoconductor drum 15. Each LED element is driven to emit light
according to the image data. The light of the LED element is
directed to the photoconductor drum 15 through a lens corresponding
to each LED element, of the lens array 63 including a plurality of
lenses. In the drawing, of the plurality of photoconductor drums
15, only the photoconductor drum 15Y is numbered for
simplicity.
[0043] FIG. 4 is a schematic view of another example structure of
the image forming unit 50 and the periphery thereof. The structure
illustrated in FIG. 4 is different from that illustrated in FIG. 2
in the configuration of the exposure device 14. FIG. 5 is a
schematic diagram illustrating another example of the detailed
configuration of the exposure device 14. FIG. 4 is a view of the
image forming unit 50 and the peripheral configuration as seen
through from a side, and FIG. 5 is a view of the exposure device 14
as seen through from above.
[0044] The exposure device 14 uses a polygon mirror 71 to deflect a
light beam to scan the photoconductor drum 15 in the main scanning
direction. The exposure device 14 deflects different color light
beams at a time using upper and lower portions of polygon mirror
faces. Further, the exposure device 14 deflects two different color
light beams at a time on the opposite sides of the polygon mirror
71 so that four color light beams are directed to the
photoconductor drums 15 of respective colors.
[0045] The exposure device 14 includes laser diode (LD) units 84-1
and 84-2 as light source units. Each of the LD units 84-1 and 84-2
includes a laser element. According to the image data, the laser
element is driven and modulated so that light beam is selectively
emitted.
[0046] The light beam emitted from the LD unit 84-1 passes through
the cylinder lens 85-1 and is directed to the polygon mirror 71
rotated by a polygon motor. The LD unit 84-1 includes LDs
respectively disposed in an upper portion and a lower portion
thereof. For example, a magenta light beam is emitted from the
upper LD and directed to the upper portion face of the polygon
mirror 71, and a yellow light beam emitted from the lower LD is
directed to the lower portion face of the polygon mirror 71.
[0047] The magenta light beam directed to the upper portion face of
the polygon mirror 71 is deflected as the polygon mirror 71
rotates. The deflected magenta light beam passes through an
f-.theta. lens 72-1 and is reflected back by mirrors 73 to 75 to
scan the photoconductor drum 15M. The yellow light beam directed to
the lower portion face of the polygon mirror 71 is deflected as the
polygon mirror 71 rotates. The deflected yellow light beam passes
through the f-.theta. lens 72-1 and is reflected back by a mirror
76 to scan the photoconductor drum 15Y.
[0048] A synchronous mirror 81-1, a synchronous lens 82-1, and a
synchronous sensor 83-1 are disposed in a non-image writing area,
which is in an end portion on a writing start side in the main
scanning direction, and outward a writing start position in the
main scanning direction. The light beams of magenta and yellow
transmitted through the f-.theta. lens 72-1 are reflected by the
synchronous mirror 81-1, collected by the synchronous lens 82-1,
and directed to the synchronous sensor 83-1. The synchronous sensor
83-1 outputs synchronization detection signals for determining the
timing of start of writing in the main scanning direction of
respective colors as the magenta and yellow light beams enter the
synchronous sensor 83-1.
[0049] The light beam emitted from the LD unit 84-2 (i.e., the
light source unit) passes through the cylinder lens 85-2 and is
directed to the polygon mirror 71 rotated by the polygon motor. An
upper portion and a lower portion of the LD unit 84-2 include LDs
respectively. For example, a cyan light beam is emitted from the
upper LD and directed to the upper portion face of the polygon
mirror 71, and a black light beam emitted from the lower LD is
directed to the lower portion face of the polygon mirror 71.
[0050] The cyan light beam directed to the upper surface of the
polygon mirror 71 is deflected by the rotation of the polygon
mirror 71. The deflected cyan light beam passes through the
f-.theta. lens 72-2 and is reflected back by the mirrors 77 to 79
to scan the photoconductor drum 15C. The black light beam directed
to the lower surface of the polygon mirror 71 is deflected by the
rotation of the polygon mirror 71, the deflected light beam of the
black color passes through the f-.theta. lens 72-2 and is reflected
back by the mirror 80 to scan the photoconductor drum 15K.
[0051] A synchronous mirror 81-2, a synchronous lens 82-2, and a
synchronous sensor 83-2 are disposed in a non-image writing area,
which is in an end portion on a writing start side in the main
scanning direction, and outward a writing start position in the
main scanning direction. The cyan and black light beams passing
through the f-.theta. lens 72-2 are reflected by the synchronous
mirror 81-2, condensed by the synchronous lens 82-2, and directed
to the synchronization sensor 83-2. The synchronous sensor 83-2
outputs synchronization detection signals for determining the
timing of start of writing in the main scanning direction of
respective colors as the cyan and black light beams enter the
synchronous sensor 83-2.
[0052] FIG. 6 is a schematic block diagram illustrating a hardware
configuration of the image forming apparatus 1. As illustrated in
FIG. 6, the image forming apparatus 1 includes, at least, a central
processing unit (CPU) 30, a read only memory (ROM) 31, a random
access memory (RAM) 32, a hard disk drive (HDD) 33, a communication
interface (I/F) 34, a control panel 35, the scanner 100, and the
image forming device 200. These elements are connected with each
other via a system bus 36.
[0053] The CPU 30 controls operation of the image forming apparatus
1. The CPU 30 executes programs stored in the ROM 31 or the HDD 33,
using the RAM 32 as a work area, to control the entire operation of
the image forming apparatus 1. Thus, the CPU 30 implements various
functions such as copying, scanning, facsimile communication, and
printing functions described above. Execution of each of these
functions (hereinafter also "job") can be stored, each time, in the
HDD 33 as operation logs of the image forming apparatus 1.
[0054] The communication I/F 34 is an interface to accept a job
from an external device via a network and transmit the image data
generated from scanning by the scanner 100 to the outside via the
network.
[0055] The control panel 35 accepts various inputs corresponding to
operation of an operator (or user) and displays various types of
information such as information indicating the operation accepted,
information indicating the operational status of the image forming
apparatus 1, and information indicating the setting of the image
forming apparatus 1. In one example, the control panel 35 is, but
not limited to, a liquid crystal display (LCD) having a touch panel
function. Another example usable is an organic electroluminescence
(EL) display having a touch panel function. In alternative to or in
addition to the LCD or the EL display, the control panel 35 can
include an operation unit such as hardware keys, a display unit
such as an indicator lamp, or both.
[0056] As described above, the scanner 100 includes the exposure
glass 11 and the reading unit 12.
[0057] The image forming device 200 includes a light source unit
40. The light source unit 40 corresponds to the LED array head 61
described with reference to FIGS. 2 and 3 and the LD unit 84-1 and
the LD unit 84-2 described with reference to FIGS. 4 and 5. The
light source unit 40 further includes light source elements 41, a
driver 42, and a light source ROM 43 (a memory).
[0058] The light source elements 41 corresponds to the LED array
element of the LED array head 61 described with reference to FIGS.
2 and 3 and laser elements respectively included in the LD units
84-1 and 84-2 described with reference to FIGS. 5 and 6. The driver
42 is, for example, a driver integrated circuit (IC). The driver 42
drives the light source element 41 to turn on according to the
image data. The light source ROM 43 stores information and settings
required for the driver 42 to drive the light source elements
41.
[0059] FIG. 7 is a block functional diagram of the image forming
apparatus 1. The image forming apparatus 1 includes a display
controller 110, a communications controller 120, a controller 130
(a processor), a reading and writing unit 140, a storing unit 150,
a correction value storing unit 160; and an input acceptance unit
170.
[0060] The display controller 110 is implemented by the CPU 30
executing a program stored in the ROM 31 or the HDD 33, using the
RAM 32 as the work area, and controls a display screen on the input
acceptance unit 170.
[0061] The communication controller 120 is implemented by the
processing of the communication I/F 34. To email the image data to
the outside or accept various types of setting information from an
external device, the communication controller 120 communicates with
the external device via a network.
[0062] The controller 130 is implemented by the CPU 30 executing a
program stored in the ROM 31 or the HDD 33 using the RAM 32 as a
work area, and executes copying, scanning, printing, or a facsimile
function, as one example of the function of the entire image
forming apparatus 1. The controller 130 includes a correction value
acquisition unit 131, a correction value transmission unit 132, a
pattern processing unit 133, an abnormality determiner 134, an
image density acquisition unit 135, a first calculation unit 136,
and a second calculation unit 137. Details of the controller 130
will be described later in a processing flow.
[0063] The reading and writing unit 140 is implemented by the CPU
30 executing a program stored in the ROM 31 or the HDD 33 using the
RAM 32 as a work area. The reading and writing unit 140 stores
various types of data in the storing unit 150 or the correction
value storing unit 160 and retrieves the data stored therein.
[0064] The storing unit 150 is implemented by the ROM 31 or the HDD
33, to store programs, document data, various setting information
necessary for the operation of the image forming apparatus 1,
operation logs of the image forming apparatus 1, and the like.
Alternatively, the storing unit 150 can be implemented by a
temporary storage function of the RAM 32.
[0065] The correction value storing unit 160 is implemented by the
light source ROM 43, to store various kinds of information and
setting used for driving the light source elements 41.
[0066] The input acceptance unit 170 is implemented by processing
of the control panel 35. The input acceptance unit 170 is
configured to display information necessary for the operation to
the operator and accept various inputs made by the operator.
[0067] Here, descriptions are given below of density unevenness in
the main scanning direction in printed images formed by the image
forming device 200 and correction of light emission amount of the
light source to eliminate or reduce the density unevenness.
[0068] If the amount of light emitted from each LED element (i.e.,
the light source element 41) in an LED head have variations, the
density of images formed by an image forming apparatus (e.g., a
printer) becomes uneven. Therefore, for example, before the
shipment of the image forming apparatus, the amount of light of
each LED element is corrected in some cases.
[0069] Specifically, before the LED head is mounted on the
apparatus, each LED element is sequentially driven, and the light
amount of each LED element is detected. Then, for example, a drive
current, drive time, or both are adjusted so that each LED element
emits a predetermined amount of light, and a correction value of
the drive current or drive time is stored in a ROM of the LED head
(e.g., the light source ROM 43). When each LED element is driven in
a state being mounted in the apparatus, the correction value is
read out from the ROM, and the drive current and the like are
adjusted based on the correction value, thereby reducing variations
in image density. Hereinafter, the correction value based on the
result of preliminary measurement of amount of light may be
referred to as "initial correction value".
[0070] When laser elements are used as the light source elements
41, similarly, the initial correction value can be stored in
advance. When laser elements are used, for example, depending on
characteristics of the f-.theta. lens, the amount of light emitted
to the photoconductor may be reduced in the end portion in the main
scanning direction.
[0071] Such reduction of light amount may be addressed by the
following method. For example, before shipment of the apparatus or
before installation of an optical system in the apparatus, the
amount of light of the optical system in the main scanning
direction is detected, and adjustment (shading correction) is
performed to keep the amount of light reaching the photoconductor
constant. The initial correction value, which is the result of such
adjustment, is stored in the ROM of the light source unit. When the
laser element is driven with the light source unit mounted on the
apparatus, adjustment is performed using the initial correction
value read out from the ROM.
[0072] However, when the light source unit is mounted on an image
forming apparatus (e.g., a printer), the above-described adjustment
using the initial correction value may be insufficient to eliminate
uneven image density. Specifically, in the light source unit being
mounted in the apparatus, variations in characteristics and shapes
of the respective elements and misalignment between the elements
may cause periodic or aperiodic fluctuations in the amount of light
emitted. To solve the uneven image density caused by such periodic
or aperiodic fluctuations, adjustment merely using the
above-described initial correction value may be insufficient.
[0073] In view of the foregoing, according to the present
embodiment, a predetermined image pattern is printed using an
apparatus on which the light source element is mounted, and the
printed pattern is read to acquire density data, based on which
correction is performed. Hereinafter, the pattern used to acquire
the density data may be referred to as "density acquisition
pattern". Adjustment based on density data may be referred to as
density correction.
[0074] With such density correction, density unevenness not
solvable with the initial correction value can be alleviated. The
density acquisition pattern includes an image density unevenness
component caused by a component of the apparatus other than the
optical system. Since the unevenness component caused by the
component other than the optical system is read in the adjustment,
such unevenness component can be adjusted to some extent in the
adjustment regarding the optical system.
[0075] The adjustment according to the present embodiment further
involves determination of whether placement of the recording medium
is proper in reading the recording medium on which the density
acquisition pattern is printed.
[0076] FIG. 8 is a flowchart illustrating a processing flow to
print a density acquisition pattern, according to an embodiment.
The correction value storing unit 160 preliminarily stores the
correction value with which the amount of light of the light source
element 41 is adjusted. The correction value can be empirically
obtained. For example, the correction value is stored in the light
source ROM 43 by the time of shipping. The correction value can be
zero.
[0077] The processing flow illustrated in FIG. 8 is executed, in
one example, when the operator instructs printing of the density
acquisition pattern. Specifically, the operator instructs, via the
control panel 35, the image forming apparatus 1 to print the
density acquisition pattern. Further, the operator can instruct
printing of the density acquisition pattern from a personal
computer (PC) being an external device. The density acquisition
pattern can be stored in advance in the storing unit 150, for
example. When printing of the density acquisition pattern is
instructed from an external device such as a PC, the density
acquisition pattern can be included in the print instruction.
[0078] The correction value acquisition unit 131 acquires a first
correction value from the correction value storing unit 160 (S1).
In a state immediately after shipment of the image forming
apparatus 1, an initial correction value set before shipment is
acquired. The correction value transmission unit 132 transmits the
acquired first correction value to the driver IC being the driver
42 (S2). The pattern processing unit 133 generates light source
drive data based on the density acquisition pattern (S3). The light
source drive data includes information and settings required for
the driver 42 to drive the light source elements 41. With the
controller 130, the drive data (e.g., drive current or drive time)
is corrected with the first correction value, and the density
acquisition pattern is printed on the recording medium (S4).
[0079] FIG. 9 is a flowchart illustrating a flow of operation to
acquire density data from the density acquisition pattern. First,
the operator places the recording medium on which the density
acquisition pattern is printed on the exposure glass 11. As the
operator instructs from the control panel 35, the image forming
apparatus 1 reads the density acquisition pattern. Alternatively,
the image forming apparatus 1 can be configured to determine what
is read is the density acquisition pattern.
[0080] As illustrated in FIG. 9, the image density acquisition unit
135 acquires density data from the scanning of the recording medium
placed on the exposure glass 11 (S5). The density data acquired at
S5 is hereinafter referred to as first density data. The controller
130 stores the first density data in the storing unit 150 (S6).
Then, the controller 130 determines whether or not the density
acquisition pattern is read normally, specifically, whether the
placement of the recording medium at the time of acquisition of the
first density data is correct (S7), When the placement is
determined as correct, the flow of operation illustrated in FIG. 9
ends.
[0081] By contrast, when the abnormality determiner 134 determines
that the placement is incorrect (reading is not normal) at S7, the
controller 130 notifies the operator of an error (abnormality) in
the reading (S8). As an example of error notification, the
controller 130 and the display controller 110 cause the control
panel 35 to display a message. The operator notified of the error
adjusts the placement of the recording medium, after which the
abnormality determiner 134 again determines whether the reading is
performed properly (S5). Through the operation illustrated in FIG.
9, the density acquisition pattern data read from the recording
medium placed properly is stored in the storing unit 150. The
abnormality determination performed at S7 will be described in
detail later.
[0082] FIG. 10 is a flow of image formation based on the density
correction. The operation illustrated in FIG. 10 is executed, for
example, when the image forming apparatus 1 accepts a print job
from an external device or the like. The first calculation unit 136
retrieves the first density data stored in the storing unit 150
(S9). Based on the first density data, the first calculation unit
136 calculates a density correction value, serving as a second
correction value, for adjusting the light emission amount of the
light source so as not to cause image density unevenness appearing
as vertical streaks or the like (S10).
[0083] The second calculation unit 137 calculates a third
correction value based on the first correction value acquired by
the correction value acquisition unit 131 and the second correction
value calculated by the first calculation unit 136 (S11). An
example of the third correction value is, but not limited to, the
sum of the initial correction value (the first correction value)
and the density correction value (the second correction value) in
an initial density adjustment after shipment.
[0084] The correction value transmission unit 132 transmits the
third correction value to the driver 42 (S12). Then, the light
emission amount of the light source unit 40 is corrected with the
third correction value (S13). Then, printing is executed (S14). As
a result, the printed image can be free from density unevenness
such as vertical stripes. In the subsequent printing, the
correction value transmission unit 132 transmits the third
correction value to the driver 42 so that an image without density
unevenness is obtained without performing the operations
illustrated in FIGS. 8, 9, and 10.
[0085] In some cases, after the first density data is stored (S6 in
FIG. 9), the image forming apparatus 1 is turned off and then
turned on again, and printing is performed. In this case, executing
the operation illustrated in FIG. 10 in an initial printing after
power-on is advantageous in that an image without density
unevenness can be obtained irrespective of changes with time of the
apparatus or environmental changes. In that case, since the first
density data has already been acquired and stored, there is no need
to again execute the operation illustrated in FIGS. 8 and 9.
[0086] By contrast, in particular, after component replacement or
the like of the image forming device 200, executing again the
operations illustrated in FIGS. 8, 9, and 10 is advantageous in
that an image without density unevenness can be obtained. In this
case, the initial correction value is preferably used as the first
correction value. For example, it is assumed that the first density
data is acquired with the density correction pattern output with
the third correction value of that time. In this case, if a
characteristic of a replaced component affecting the image density
unevenness varies in the opposite directions before and after the
replacement, the span of correction increases. Therefore, to reduce
the possibility of degradation of correction accuracy, use of the
initial correction value is preferred.
[0087] There may be cases where correction of density unevenness is
unnecessary or the density correction fails to alleviate or worsens
the density unevenness. In such a case, the controller 130 can
obviate the operation of the second calculation unit 137 so that
the driver 42 drives the light source elements 41 with the first
correction value. Alternatively, resetting the first density data
in the storing unit 150 enables the driver 42 to drive the light
source elements 41 with the first correction value.
[0088] FIGS. 11A and 11B are graphs illustrating image density
distributions in the main scanning direction of an output result
based on the first correction value of the density acquisition
pattern and an output result based on the third correction value.
In this example, an LED array is used as the light source. FIG. 11A
illustrates the result of printing according to the light source
drive data corrected with the first correction value, and FIG. 11B
illustrates the result of printing according to the light source
drive data corrected with the third correction value.
[0089] In FIG. 11A, the solid line indicates the density
distribution and the chain double-dashed line indicates the average
value of the density data. According to FIG. 11A, when the light
source drive data is corrected with the first correction value, the
variations in the image density indicated by the solid line from
the average value is large. This is because the image density
unevenness caused by the light amount variations among the LED
elements are not fully eliminated, and, in addition, the image
density unevenness caused by the components, such as the
photoconductor drum 15 and the transfer belt 17, of the image
forming device 200 is not corrected. By contrast, FIG. 11B
illustrates the result of density correction corresponding to both
the light amount variations among the LED elements and the density
unevenness caused by the components of the image forming device
200. Accordingly, a uniform image without density unevenness is
obtained.
[0090] FIG. 12 is a schematic view of a recording medium on which a
density acquisition pattern 500 according to an embodiment is
printed; The density acquisition pattern 500 includes a continuous
area printed in a substantially rectangular area that is shorter in
the direction of conveyance of the recording medium P (hereinafter
"sheet conveyance direction") identical to the sub-scanning
direction (indicated by arrow AR2) and longer in the direction
(main scanning direction) orthogonal to the sheet conveyance
direction. FIG. 12 illustrates a print result of a halftone image
that is uniform in the sub-scanning direction and the main scanning
direction, obtained by density correction based on the first
correction value. Specifically, FIG. 12 schematically illustrates a
case where the optical variations in the main scanning direction of
the LED head mounted in the apparatus and image density unevenness,
such as the vertical streaks or bands, resulting from variations
unique to the components of the image forming device 200 are not
corrected in the correction based on the first correction value,
resulting in uneven image density of the uniform halftone
image.
[0091] With reference to FIG. 12, a method of acquiring the first
density data will be described. Density data can be acquired in a
given width with a minimum resolution being a dot range defined by
arrow X in the main scanning direction and arrow Y in the sub
scanning direction. The acquired density data is stored, for each
range, in the light source ROM 43 (the memory). At the time of
reading out, a given area can be designated to be read out, to
acquire the density data of the given area.
[0092] FIG. 13 is a flowchart illustrating a flow of operation to
determine abnormality (placement error) in reading. The flowchart
illustrated in FIG. 13 is a detailed illustration of S7 illustrated
in FIG. 9. The abnormality determiner 134 determines whether the
position and orientation of the recording medium P are proper at
S71 and determines whether inclination of the recording medium P is
proper at S72.
[0093] FIG. 14 illustrates an example of a density acquisition
pattern formation area and areas for determining abnormality in
reading (placement error).
[0094] FIG. 14 illustrates sheets PA and PB, as recording media,
different in size. The sheet PB is larger than the sheet PA. On the
exposure glass 11, a corner of the sheet PA or PB is aligned with a
reference position RP. In FIG. 14, the density acquisition pattern
500 on the sheet PB is longer by a length L in the main scanning
direction than the density acquisition pattern 500 on the sheet PA.
That is, the width of the density acquisition pattern 500 in the
main scanning direction is set according to the sheet size. This is
because the density data can be obtained over a wider range
irradiated by the light source when the density acquisition pattern
500 is printed longer in the main scanning direction. For example,
in the case of an LED array, density data can be acquired for a
greater number of light source elements in correcting the density
unevenness.
[0095] However, blank areas T (sometimes referred to as trim areas
or margins) having a constant width are secured at both ends of the
sheet in the main scanning direction. If the density acquisition
pattern 500 extends to the end of the sheet, the following
inconvenience may occur. If the position of the printing is shifted
even slightly, the image forming device 200 may be smeared with a
portion of toner to be transferred onto the sheet.
[0096] Additionally, on both the sheets PA and PB (the recording
media), the density acquisition pattern 500 (hereinafter may be
simply "pattern") is formed in a region shifted from the center in
the sub-scanning direction, and the position varies depending on
sheet size. The reason will be described later.
[0097] In FIG. 14, each of the sheets PA and PB includes a first
area 1A (a pattern presence determination area) and a second area
2A (a pattern absence determination area, collectively "abnormality
determination areas") for determining an abnormality or error in
placement of the recording medium P, using the density data read
from these areas by the scanner 100, of the first density data
stored in the storing unit 150.
[0098] The description referring to FIG. 14 continues. Here, the
reading unit 12 illustrated in FIG. 1 reads the image density of
the same area on the exposure glass 11 based on the device
configuration of the scanner 100. By contrast, placement of the
recording medium (sheet) placed on the exposure glass 11 may be
improper with a wrong orientation or an inclination due to an error
of the operator, a malfunction of the ADF 13, or the like. FIG. 14
illustrates the positions of the areas for acquiring density data,
on the sheet on which the density acquisition pattern 500 is
printed, in a case where placement of the sheet on the exposure
glass 11 is correct. If the position of the sheet deviates from the
position illustrated in FIG. 14, the density data at the position
on the sheet shifted from the position illustrated in FIG. 14 is
acquired in each area.
[0099] That is, when the placement of the sheet on the exposure
glass 11 is correct, as illustrated in FIG. 14, density data
corresponding to the density acquisition pattern 500 is to be
obtained from the first area 1A. Additionally, from the second area
2A, density data including both a value corresponding to the
density acquisition pattern 500 and a value corresponding to the
blank area T without the density acquisition pattern 500 are to be
obtained.
[0100] Therefore, when the density data acquired from the first
area 1A does not include the value corresponding to the density
acquisition pattern 500, presumably, the placement of the recording
medium P being read is incorrect. Similarly, when the density data
acquired from the second area 2A does not include the value
corresponding to the blank area T, presumably, the placement of the
recording medium P being read is incorrect.
[0101] As described above, the size of the density acquisition
pattern 500 varies depending on the sheet (sheet size). Therefore,
for example, the controller 130 can be configured to select the
abnormality determination areas corresponding to the size of the
sheet on which the density acquisition pattern 500 is printed most
recently. With such a setting, density correction based on the
density acquisition pattern 500 corresponding to a wrong sheet size
can be inhibited.
[0102] As an example, settings of the abnormality determination
areas corresponding to the respective sheet sizes are stored in the
storing unit 150. The controller 130 refers to the sheet setting or
the like at the time of most recent printing of the density
acquisition pattern 500 from the operation logs of the image
forming apparatus 1. Then, the controller 130 selects the
abnormality determination areas corresponding to the size of the
sheet used in the most recent printing of the density acquisition
pattern 500.
[0103] FIG. 15 is a flowchart illustrating an example of detection
of improper sheet placement according to an embodiment. This flow
is mainly executed by the abnormality determiner 134.
[0104] First, the reading and writing unit 140 retrieves, from the
storing unit 150 or the like, the sheet settings (i.e., latest
print setting) used last printing of the density acquisition
pattern by the image forming device 200. The first and second areas
1A and 2A are selected corresponding to the sheet type (S71-1).
[0105] The density data of the selected first area 1A is acquired
(S71-2), and the presence or absence of the pattern is determined
from the density data (S71-3). For example, to check the presence
or absence of the pattern, a threshold of the density value is
set.
[0106] When the first area 1A includes the pattern, the abnormality
determiner 134 acquires the density data of the second area 2A
(S71-4). If the pattern is not in the first area 1A, the
abnormality determiner 134 determines that the position or
orientation of the recording medium P is improper and sets the
detection result to "abnormal" (S71-7).
[0107] Following S71-4, the abnormality determiner 134 determines
whether the density data of the second area 2A includes the value
corresponding to the blank area T (S71-5). If the determination is
"Yes", the abnormality determiner 134 sets the detection result to
"normal" (S71-6). If not, the detection result is set to "abnormal"
(S71-7).
[0108] Alternatively, at S71-4, the abnormality determiner 134 can
determine whether the density data of the second area 2A includes
both the value corresponding to the pattern and the value
corresponding to the blank area T. In that case, the abnormality
determiner 134 can determine whether the second area 2A corresponds
to an end of the density acquisition pattern 500. In addition, the
operation flow illustrated in FIG. 15 is not limited to the
determination of abnormality in position and orientation, and,
according to the operation flow illustrated in FIG. 15, the
abnormality determiner 134 can estimate the inclination of the
recording medium P, thereby determining the placement error of the
recording medium, with the density acquisition pattern 500 and
selecting of the first and second areas 1A and 2A.
[0109] FIG. 16 illustrates another example of the density
acquisition pattern formation area and the abnormality
determination areas.
[0110] FIG. 16 illustrates a third area 3A (a first boundary area)
and a fourth area 4A (second boundary area) for determining
abnormality in placement (placement error) of the recording medium,
specifically, an inclination of the recording medium.
[0111] Both the third area 3A and the fourth area 4A are
substantially rectangular and are identical to each other in length
in the main scanning direction, position in the sub-scanning
direction, and length in the sub-scanning direction. In the
sub-scanning direction (vertical direction in FIG. 16), both the
third and fourth areas 3A and 4A extend from a region slightly
above the upper end of the density acquisition pattern 500, that
is, a position free from the density acquisition pattern 500, to a
region overlapping the density acquisition pattern 500.
[0112] By contrast, in the main scanning direction, the third and
fourth areas 3A and 4A are different in position from each other.
The third area 3A is closer to one end of the density acquisition
pattern 500, whereas the fourth area 4A is closer to the opposite
end thereof. The distances from the ends of the density acquisition
pattern 500 to the areas are substantially the same.
[0113] As described above, since the density acquisition pattern
500 varies depending on the sheet size, the third and fourth areas
3A and 4A are also set according to the sheet size.
[0114] FIG. 17 is an enlarged view of the third areas 3 and 4
serving as the abnormality determination areas and the surroundings
thereof. Each of the third and fourth areas 3A and 4A are divided
into blocks .beta., which are minimum units for acquiring an image
density value in the main scanning direction X and the sub-scanning
direction Y. In one example, the divided blocks .beta. are numbered
from .beta.1 to .beta.1 to .beta.2 in the order from the divided
block .beta. closest to the reference point in the sub-scanning
direction.
[0115] FIG. 18 is a flowchart illustrating an example of detection
of improper sheet placement according using the abnormality
determination areas illustrated in FIG. 17. The flow in FIG. 18 is
mainly performed by the abnormality determiner 134 to determine an
inclination (wrong orientation) regarding the placement of the
recording medium.
[0116] The abnormality determiner 134 acquires density data of the
blocks .beta. in the third area 3A in FIG. 17, sequentially from
the block 31, and assigns, as a boundary .beta.a, the first one of
the blocks .beta. including the density acquisition pattern 500
(S72-1). Regarding the fourth area 4A, similarly, the first one of
the blocks .beta. including the density acquisition pattern 500 is
assigned as a boundary .beta.b (S72-2). The abnormality determiner
134 determines whether the difference between a and b indicating
the boundary position between the density acquisition pattern area
and the outside thereof is smaller than a threshold, e.g., 3
(S72-3). When the difference between a and b is equal to or greater
than the threshold (No at 72-3), the abnormality determiner 134
determines the inclination being abnormal (S72-5). Other than that,
the inclination is determined as normal (S72-4).
[0117] It is assumed that the third and fourth areas 3A and 4A are
selected together with the first and second areas 1A and 2A at
S71-1 in FIG. 15 which has been performed earlier. Alternatively,
when the operation flow illustrated in FIG. 18 is performed
independently of the operation flow illustrated in FIG. 15 or
before execution of the operation flow illustrated in FIG. 15, a
process corresponding to S71-1 in FIG. 15 is performed before S72-1
in FIG. 18.
[0118] With reference to FIGS. 19A to 21B, descriptions are given
below of examples of the density acquisition pattern on the
recording medium, placement of the recording medium on the exposure
glass 11, and determination results in the respective examples. In
common among FIGS. 19A to 21B, "sheet PA" and "sheet PB" are
different in size, and the sheet PB is larger than the sheet
PA.
[0119] FIGS. 19A and 19B illustrate first explanatory examples of
placement of the recording medium and determination results of the
placement. Specifically, in this example, the recording medium is
placed upside down in the sub-scanning direction.
[0120] On each of the sheet PA in FIG. 19A and the sheet PB in FIG.
19B, the density acquisition pattern 500 sized according to the
sheet size is printed. The density acquisition pattern 500 on each
of the sheets PA and PB is shifted from the center of the sheet PA
or PB in the sub-scanning direction (lateral direction in FIGS. 19A
and 19B). With such a shifted position, on the sheet PA or PB
placed upside down in the sub-scanning direction as illustrated in
FIGS. 19A and 19B, the density value of the first area 1A
corresponds to the blank area T. Therefore, in both of FIGS. 19A
and 19B, the determination result is "abnormal".
[0121] FIGS. 20A and 20B illustrate second explanatory examples of
placement of the recording medium and determination results of the
placement. As described above, the areas are determined based on
the sheet size on which the density acquisition pattern 500 is
printed most recently. However, for example, the operator may
mistakenly places, not the sheet on which the density acquisition
pattern has been printed most recently, but a different size sheet
on which the pattern has been printed at another timing, which is
the example illustrated in FIGS. 20A and 20B.
[0122] FIG. 20A illustrates a case where the density acquisition
pattern 500 has been printed on the sheet PB for density correction
performed before the density acquisition pattern 500 is printed on
the sheet PA, and the sheet PB is mistakenly placed on the exposure
glass 11. FIG. 20B illustrates a case where the density acquisition
pattern 500 has been printed on the sheet PA for density correction
performed before printing on the sheet PB, and the sheet PA is
mistakenly placed on the exposure glass 11. In both of FIGS. 20A
and 20B, the position of the density acquisition pattern 500 and
the position of the abnormality determination areas are different
in the sub-scanning direction. Accordingly, the density acquisition
pattern 500, which should be present in the first area 1A, is
absent in the first area 1A, and the placement is determined as
abnormal.
[0123] FIGS. 21A and 21B illustrate third explanatory examples of
placement of the recording medium and determination results of the
placement. In both of FIGS. 21A and 21B, the size of the recording
medium on which the density acquisition pattern 500 is printed is
wrong. Specifically, in FIG. 21A, the density acquisition pattern
500 to be printed on sheet PB is mistakenly printed on sheet PA,
and in FIG. 21A, the density acquisition pattern 500 to be printed
on sheet PA is mistakenly printed on sheet PB. For example, such a
mismatch occurs when the density acquisition pattern 500 is printed
in a state where the settings of the sheet tray does not match the
size of the sheets stored in that sheet tray due to a setting
mistake or the like made to the image forming apparatus 1. In the
case of FIG. 21A, the placement is determined as "abnormal", and,
in the case of FIG. 21B, the placement is determined as "normal",
which will be described below.
[0124] In the example illustrated in FIG. 21A, the density
acquisition pattern 500 is printed on a sheet size smaller than the
sheet size regarding which the density correction is to be
performed. The first area 1A includes the density acquisition
pattern 500, but the second area 2A does not include the blank area
T. Accordingly, the abnormality determiner 134 determines the
placement as "abnormal" based on the determination of the density
data corresponding to the second area 2A. Although the first
density data is to be acquired for printing on the sheet PB, the
sheet PA is smaller than the sheet PB, and both ends of the density
acquisition pattern 500 are not printed on the sheet PA. In this
example, since the first density data necessary for correcting the
density unevenness on the sheet B is not fully acquired, a
placement error (or abnormality in reading) should be reported.
[0125] By contrast, in the example illustrated in FIG. 21B, the
density acquisition pattern 500 is printed on a sheet size larger
than the sheet size regarding which the density correction is to be
performed. The first area 1A includes the density acquisition
pattern 500, and the second area 2A includes the blank area T.
Accordingly, the abnormality determiner 134 determines the
placement as "normal". In this example, in the main scanning
direction, the entire density acquisition pattern 500 is printed on
the sheet PB, and the first density data for the density correction
can be fully acquired. Accordingly, a placement error (or
abnormality in reading) is not reported and acquisition of the
first density data is performed.
[0126] As described with reference to FIGS. 19A to 21B, the density
acquisition pattern 500 and the abnormality determination areas can
be set for each of sheet sizes accommodated by the scanner 100 so
that the abnormality determination can be made with the sheet size
distinguished.
[0127] FIGS. 22A and 22B illustrate example density acquisition
patterns considering shock jitter. Similar to FIGS. 19A to 21B,
"sheet PA" and "sheet PB" are different in size, and the sheet PB
is larger than the sheet PA.
[0128] Shock jitter is a positional deviation of an image caused by
fluctuations in the speed of the transfer belt 17 and the resulting
time lag in primary transfer. In a region SJ in FIGS. 22A and 22B,
where optical system jitter occurs, there is a possibility of
positional deviation of the density acquisition pattern 500, and
accurate density data is not acquired.
[0129] The position where optical system jitter occurs varies
depending on sheet size and sheet thickness. Accordingly, the
region SJ where optical system jitter occurs is empirically grasped
for each sheet size that may be used in the scanner 100, and the
density acquisition pattern 500 can be set at a position avoiding
the region SJ.
[0130] The above-described embodiments are illustrative and do not
limit the present invention. Thus, numerous additional
modifications and variations are possible in light of the above
teachings. For example, elements and/or features of different
illustrative embodiments may be combined with each other and/or
substituted for each other within the scope of the present
invention. Any one of the above-described operations may be
performed in various other ways, for example, in an order different
from the one described above.
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